1. Field of the Invention
The present invention relates to a semiconductor package and, in particular, to a package for preventing solder from flowing at bonding in the process of fabricating semiconductor devices.
2. Description of the Related Art
FIG. 5 is a perspective view illustrating a conventional semiconductor device. A base ceramic member 1 is positioned on a heat radiating board 8. A frame ceramic member 5 having an opening 5a is positioned on the base ceramic member 1. Metallized layers 12a and 12b are formed on the frame ceramic member 5. Leads 6a and 6b are disposed on the metallized layers 12a and 12b respectively. Metallized layers 2 and 14 are formed on the base ceramic member 1 inside the opening 5a of the frame ceramic member 5 and a semiconductor chip 9 is mounted on the metallized layer 2 with solder 10. Numeral 11 denotes a fine metallic wire.
A section of the mounted semiconductor chip 9 is shown in FIG. 6. An Au-plated layer 4 is formed on the metallized layer 2 which is positioned on the base ceramic member 1 via an Ni-plated layer 3. The semiconductor chip 9 is fixedly mounted on the Au-plated layer 4 by the solder 10.
The semiconductor devices described above are manufactured in the following way. First, ceramics such as beryllia are metallized to form metallized layers 2 and 14 in arbitrary patterns Then, by baking these layers, the base ceramic member 1 is formed. At this time, the metallized layer 14 reaches the rear surface of the base ceramic member 1. Next, the Ni-plated layer 3 is formed on the metallized layers 2 and 14 as a surface preparation, then the frame ceramic member 5 and the heat radiating board 8 are brazed on the Ni-plated layer 3. Further, the Au-plated layer 4 or an Ag-plated layer is formed on the Ni-plated layer 3 positioned in a die-pad area 13 and a wire bonding area, thus manufacturing a package. The semiconductor chip 9 is fixedly mounted on the die-pad area 13 of this package by the solder 10 and a fine metallic wire 11 is bonded to the required portions. Then the package is sealed, completing the fabrication of the semiconductor device.
However, since the semiconductor chip 9 is carried on board, as shown in FIG. 6, generally, an extension of the solder 10 called solder flow occurs on the die-pad area 13. For this reason, the fine metallic wire 11 for electrically connecting a bottom-surface electrode of the semiconductor chip 9 has to be bonded onto the solder flow. It is known that the adhesion force of the fine metallic wire 11 bonded onto the solder flow is very weak, and there is the possibility that the fine metallic wire 11 will be separated from the solder flow due to thermal stress during use or the like, causing a defective connection. Also, bonding may sometimes be impossible.
As described above, a conventional semiconductor package has a problem in that reliability decreases as the result of solder flow.